A floating point unit (FPU) is generally employed as a processor or co-processor for performing calculation intensive manipulations, found in floating point arithmetic, such as addition and multiplication. A first type of FPU has separate units for “multiply” operations and “add” operations. A second type of FPU comprises a single unit which performs both operations. In the FPU, the additive and multiplicative arithmetical operations can be expressed as “A times B plus C,” with “A,” “B” and “C” as separate inputs.
An FPU, such as the second type of FPU, has a large number of circuits. Two of these circuits are the “multiplier” and the “aligner.” Generally, the multiplier inputs two numbers, “A” and “B”, to be multiplied, and outputs two other numbers. The two numbers that are outputted, if added together, equal the multiplication of the first two numbers. The “aligner” circuit generally looks at the exponents of all three operands, and then shifts the fraction of the addend accordingly.
In conventional FPUs, the multiplier creates two values “A1” and “B1” from the inputs “A” and “B.” In other words, A times B equals A1 plus B1. Furthermore, for addition, the aligner is employed to have the added operand, comprising a mantissa and an exponent, to be expressed as the same order of magnitude as the product A times B. In other words, a C value of 3.04×103 can be expressed as 3040. Therefore, the FPU generates internal values of A1, B1 and C1, wherein C1 is a compatible order of magnitude to A1 and B1. A1, B1 and C1 are input into a 3:2 adder, and two numbers result, D and E. D and E are added together, the result of which equals A times B plus C. This result is then sent to a normalizer and rounder. Furthermore, in many designs, the FPU is also used for the integer multiply operations, not just on floating point data.
However, employing the FPU in this manner can result in significant power demands, in part due to the extensive calculations performed. These power demands can then generate heat. Heat generated by an FPU can place design and use limitations upon the FPU. Therefore, what is needed is an FPU that solves at least some of the power use and heat generation disadvantages of conventional FPUs.